Augmentation of soft tissue using synthetic materials such as silicone or polytetrafluoroethylene (PTFE) is well known in the art. U.S. Pat. No. 5,876,447 to Arnett discloses the use of silicone implants for facial plastic surgery. However, such synthetic materials are foreign to the host tissue, and cause an immunological response resulting in the encapsulation of the implant and scarring of the surrounding tissues. Thus, the implant may produce additional functional or aesthetic problems.
Soft tissue augmentation using biopolymers such as collagen or hyaluronic acid has also been described. For example, U.S. Pat. No. 4,424,208 to Wallace et al. discloses methods of augmenting soft tissue utilizing collagen implant material. In addition, U.S. Pat. No. 4,965,353 to della Valle et al. discloses esters of hyaluronic acid that can be used in cosmetic surgery. However, these biopolymers are also foreign to the host tissue, and cause an immunological response resulting in the reabsorption of the injected material. Biopolymers are therefore unable to provide long-term tissue augmentation. Overall, the use of biopolymers or synthetic materials has been wholly unsatisfactory for the purpose of augmenting soft tissue.
Soft tissue augmentation using cell-based compositions has also been developed. U.S. Pat. No. 5,858,390 to Boss, Jr. discloses the use of autologous dermal fibroblasts for the treatment of cosmetic and aesthetic skin defects. Although this treatment avoids the problems inherent in the implantation or injection of synthetic materials or biopolymers, it results in other complications. Because fibroblasts produce collagen, the cells can cause the stiffening and distortion of the tissues surrounding the implant site.
The use of autologous fat cells as an injectable bulking agent has also been described (For review, see K. Mak et al., 1994, Otolaryngol. Clin. North. Am. 27:211-22; American Society of Plastic and Reconstructive Surgery: Report on autologous fat transplantation by the ad hoc committee on new procedures, 1987, Chicago: American Society of Plastic and Reconstructive Surgery; A. Chaichir et al., 1989, Plast. Reconstr. Surg. 84: 921-935; R. A. Ersek, 1991, Plast. Reconstr. Surg. 87:219-228; H. W. Horl et al., 1991, Ann. Plast. Surg. 26:248-258; A. Nguyen et al., 1990, Plast. Reconstr. Surg. 85:378-389; J. Sartynski et al., 1990, Otolaryngol. Head Neck Surg. 102:314-321. However, the fat grafting procedure provides only temporary augmentation, as injected fat is reabsorbed into the host. In addition, fat grafting can result in nodule formation and tissue asymmetry.
Myoblasts, the precursors of muscle fibers, are mononucleated muscle cells that fuse to form post-mitotic multinucleated myotubes, which can provide long-term expression and delivery of bioactive proteins (T. A. Partridge and K. E. Davies, 1995, Brit. Med. Bulletin 51:123-137; J. Dhawan et al., 1992, Science 254: 1509-12; A. D. Grinnell, 1994, Myology Ed 2, A. G. Engel and C. F. Armstrong, McGraw-Hill, Inc., 303-304; S. Jiao and J. A. Wolff, 1992, Brain Research 575:143-7; H. Vandenburgh, 1996, Human Gene Therapy 7:2195-2200).
Cultured myoblasts contain a subpopulation of cells that show some of the self-renewal properties of stem cells (A. Baroffio et al., 1996, Differentiation 60:47-57). Such cells fail to fuse to form myotubes, and do not divide unless cultured separately (A. Baroffio et al., supra). Studies of myoblast transplantation (see below) have shown that the majority of transplanted cells quickly die, while a minority survive and mediate new muscle formation (J. R. Beuchamp et al., 1999, J. Cell Biol. 144:1113-1122). This minority of cells shows distinctive behavior, including slow growth in tissue culture and rapid growth following transplantation, suggesting that these cells may represent myoblast stem cells (J. R. Beuchamp et al., supra).
Myoblasts have been used as vehicles for gene therapy in the treatment of various muscle- and non-muscle-related disorders. For example, transplantation of genetically modified or unmodified myoblasts has been used for the treatment of Duchenne muscular dystrophy (E. Gussoni et al., 1992, Nature, 356:435-8; J. Huard et al., 1992, Muscle & Nerve, 15:550-60; G. Karpati et al., 1993, Ann. Neurol., 34:8-17; J. P. Tremblay et al., 1993, Cell Transplantation, 2:99-112; P. A. Moisset et al., 1998, Biochem. Biophys. Res. Commun. 247:94-9; P. A. Moisset et al., 1998, Gene Ther. 5:1340-46). In addition, myoblasts have been genetically engineered to produce proinsulin for the treatment of Type 1 diabetes (L. Gros et al., 1999, Hum. Gen. Ther. 10:1207-17); Factor IX for the treatment of hemophilia B (M. Roman et al., 1992, Somat. Cell. Mol Genet. 18:247-58; S. N. Yao et al., 1994, Gen. Ther. 1:99-107; J. M. Wang et al., 1997, Blood 90:1075-82; G. Hortelano et al., 1999, Hum. Gene Ther. 10:1281-8); adenosine deaminase for the treatment of adenosine deaminase deficiency syndrome (C. M. Lynch et al., 1992, Proc. Natl. Acad. Sci. USA, 89:1138-42); erythropoietin for the treatment of chronic anemia (E. Regulier et al., 1998, Gene Ther. 5:1014-22; B. Dalle et al., 1999, Gene Ther. 6:157-61), and human growth hormone for the treatment of growth retardation (K. Anwer et al., 1998, Hum. Gen. Ther. 9:659-70).
Myoblasts have also been used to treat muscle tissue damage or disease, as disclosed in U.S. Pat. No. 5,130,141 to Law et al., U.S. Pat. No. 5,538,722 to Blau et al., and application U.S. Ser. No. 09/302,896 filed Apr. 30, 1999 by Chancellor et al. In addition, myoblast transplantation has been employed for the repair of myocardial dysfunction (C. E. Murry et al., 1996, J. Clin. Invest. 98:2512-23; B. Z. Atkins et al., 1999, Ann. Thorac. Surg. 67:124-129; B. Z. Atkins et al., 1999, J. Heart Lung Transplant. 18:1173-80).
In spite of the above, in most cases, primary myoblast-derived treatments have been associated with low survival rates of the cells following transplantation due to migration and/or phagocytosis. To circumvent this problem, U.S. Pat. No. 5,667,778 to Atala discloses the use of myoblasts suspended in a liquid polymer, such as alginate. The polymer solution acts as a matrix to prevent the myoblasts from migrating and/or undergoing phagocytosis after injection. However, the polymer solution presents the same problems as the biopolymers discussed above. Furthermore, the Atala patent is limited to uses of myoblasts in only muscle tissue, but no other tissue.
Thus, there is a need for other, different soft tissue augmentation materials that are long-lasting, compatible with a wide range of host tissues, and which cause minimal inflammation, scarring, and/or stiffening of the tissues surrounding the implant site. Accordingly, the muscle-derived progenitor cell-containing compositions of the present invention are provided as improved and novel materials for augmenting soft tissues. Further provided are methods of producing muscle-derived progenitor cell compositions that show long-term survival following transplantation, and methods of utilizing MDC and compositions containing MDC to treat various aesthetic and/or functional defects, including, for example, dermatological conditions or injury, and muscle weakness, injury, disease, or dysfunction.
It is notable that prior attempts to use myoblasts for non-muscle soft tissue augmentation were unsuccessful (U.S. Pat. No. 5,667,778 to Atala). Therefore, the findings disclosed herein are unexpected, as they show that the muscle-derived progenitor cells according to the present invention can be successfully transplanted into non-muscle and muscle soft tissue, including epithelial tissue, and exhibit long-term survival. As a result, MDC and compositions comprising MDC can be used as a general augmentation material for muscle or non-muscle soft tissue augmentation, as well as for bone production. Moreover, since the muscle-derived progenitor cells and compositions of the present invention can be derived from autologous sources, they carry a reduced risk of immunological complications in the host, including the reabsorption of augmentation materials, and the inflammation and/or scarring of the tissues surrounding the implant site.
Although mesenchymal stem cells can be found in various connective tissues of the body including muscle, bone, cartilage, etc. (H. E. Young et al., 1993, In Vitro Cell Dev. Biol. 29A:723-736; H. E. Young, et al., 1995, Dev. Dynam. 202:137-144), the term mesenchymal has been used historically to refer to a class of stem cells purified from bone marrow, and not from muscle. Thus, mesenchymal stem cells are distinguished from the muscle-derived progenitor cells of the present invention. Moreover, mesenchymal cells do not express the CD34 cell marker (M. F. Pittenger et al, 1999, Science 284:143-147), which is expressed by the muscle-derived progenitor cells described herein.